The present exemplary embodiment relates broadly to the art of microcell structures, and, more particularly, to a method of sealing cells within a microstructure using adhesive microcapsules. It finds particular application in conjunction with sealing the individual cells of an array of cell microstructures in displays and other similar output devices, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is equally applicable for use in other amenable applications and/or environments in which individually sealed microstructures are used and in which excess liquid adhesive would be a disadvantage. Suitable microstructures include microcells, microchambers, microchannels and microtubes, for example, and any other suitably sized well, cavity or structural configuration regardless of how formed.
A variety of products are known to utilize microstructural cell arrays. Such products include elecrophoretic displays, for example, which retain electrophoretic ink within arrays of cells formed between sheets of a relatively rigid substrate, such as glass, for example. Using rigid sheets of glass enables a compression seal to be formed with the walls of each cell by securing and sealing the sheets of glass to one another along the periphery thereof, such as on a frame, for example. Thus, the cell walls are compressed between the glass forming compression or other fluid-tight seals that retain the electrophoretic ink in the cells. This is an example of a known construction of a rigid display.
Recent efforts have been directed to the development of flexible constructions, such as products referred to as “electronic paper” and/or other pliable displays and graphical output products, for example. Obviously, such constructions cannot be formed from sheets of glass or other relatively rigid materials. Rather, these flexible constructions utilize pliable sheets or substrates between which the microcells are captured. While on rigid displays only the perimeter of the construction is generally sealed, more flexible constructions require that the individual microcells are each substantially sealed. Otherwise, the contents of the individual microcells will flow or otherwise shift between the cells resulting in an undesirable performance and/or appearance of the flexible product.
In one known method of sealing the microcells, a wall microstructure is provided on a first flexible substrate. A second flexible substrate is coated with a substantially continuous layer of adhesive or sealant and positioned on the end portion of the wall microstructure to effectively seal the microcells. The continuous layer of adhesive, however, is typically formed from a liquid. This is a significant disadvantage because the excess liquid adhesive that is not used in forming the bond with the wall microstructure of the microcells tends to migrate into or otherwise intermix with the contents of the cells. This typically undesirably affects the substance captured within the cells.
For example, where the content of the cells is an electrophoretic ink, the adhesive can flow into and mix with the liquid ink and, once solidified, can limit particulate migration reducing the performance of the electrophoretic ink. The cured adhesive can also have other undesirable effects, such as reducing optical clarity and/or contrast of the cells, for example. Furthermore, where the contents of the cells is a dry, powdery substance, such as toner or charged pigments in general, biological powders such as spores, or light-emitting powders such as phosphors, for example, the excess adhesive tends to undesirably agglomerate and/or solidify the particles, again, reducing the performance and operation of the cells. In still another application, the excess adhesive can become affixed to or otherwise interfere with the operation of a micromechanical or microelectromechanical device, such as a microaccelerometer, a micromirror device, or a pressure sensor, for example, that is disposed within a cell. One example of such an application would include packaging and/or hermetic sealing of the micromechanical or microelectromechanical device.
In another known method of sealing microcells, the use of a second substrate is avoided and each cell is sealed with a layer of liquid adhesive. Such constructions, however, also have a number of disadvantages. One such disadvantage is that the method is only practical when used in association with liquid contents of the cells. This is due, at least in part, to the problems and disadvantages discussed above with regard to the use of a liquid adhesive in association with powdered substances and/or microelectromechanical devices. Another disadvantage is that the liquid adhesive and the liquid cell contents must have specific properties relative to one another that, thus, limit the wide application and use of this method. For example, in one application, it is desired for the liquid adhesive to have a lower specific gravity than the liquid contents of the cells. In this way, the liquid adhesive will “float” on the contents of the cells and can thereafter be cured to effectively seal the open end of the cells.